The present invention relates to a fuel injection valve (injector) for the gas direct injection type engine in which fuel is injected directly into the cylinder of the engine.
As for the gasoline engine satisfying such social needs as high power, high fuel-efficiency and low pollution, engines using fuel injection valves of gas direct injection type (gas direct injection type gasoline engine) are remarked. Though the basic concept of this gasoline engine was born in many years ago, there have remained many problems to be solved such as high-pressure injection technology, pressure tightness and heat resistance in order to implement those engines for injecting fuels directly into the combustion chamber, however, the state-of-the-art in technology enables mass-production by today's advances in control technology and production technology, and thus, the individual auto makers go into the commercial-base production phase or into the R&D-base experimental manufacture phase.
The fuel injection valve of gas direct injection type is composed of a nozzle having a fuel injection port facing directly to the fuel chamber (the cylinder inside the engine), a valve body for opening and closing the fuel channel, a magnet coil for closing the valve body (for suction), a spring for closing the valve, and a yoke and a core for forming the magnetic circuit. In addition, a swirler (fuel swirling means) for providing the fuel at the upper stream of the valve sheet with a swirling force and a spring adjuster for adjusting the quantity of dynamic fuel injection are included.
A structure characteristic of this fuel injection valve of gas direct injection type includes that, as the fuel pressure reaches such a high value that 3 to 10 MPa in order to establish the grain refinement of the fuel spray liquid drop (for reducing the evaporation time) and the high efficiency in fuel injection (for reducing the fuel injection time), the pressure tightness and the oil tightness are enhanced in comparison with the fuel injection valve of conventional gas injection type with the fuel pressure being about 0.3 Mpa, and that the heat resistance and the gas tightness are enhanced because the nozzle is exposed directly to the combustion gas.
The characteristic and shape of the fuel spray injected out from the fuel injection valve is very important n the combustion operation in the gasoline engine of gas direct injection type. The engine combustion mode includes the homogeneous combustion and the stratified combustion, and those modes are shown in FIG. 8.
The homogeneous combustion is that the fuel injected during the intake stroke of the engine cycle, and that the fuel-air mixture in the combustion chamber is made to be homogenized with a theoretical air fuel ratio (A/F=15) through the compression stroke up to the ignition and combustion operation, which may increases the volumetric efficiency because the gasoline removes the latent heat of vaporization from the intake air and cools down the intake air, and may attain a higher output than the conventional port injection engine because the temperature of the combustion gas decreases. As it is required to diffuse the fuel wholly in the combustion chamber for establishing a uniform combustion with sprayed fuel, a wide and uniform fuel spray (mixed gas) is necessary, and therefore, it is preferable that the spray velocity is low so that fuel spray may not stick to the cylinder wall and the liquid membrane may not be developed. The uniform combustion mode is used for respecting the engine output when accelerated operations and high load operations.
A stratified combustion is such a combustion mode that a fuel is injected while a compression stroke, and the flammable mixed gas is concentrated around the ignition plug by means of air flows such as swirl and/or tumble flows and a cavity at the piston head, and an air layer is formed around the mixed gas and an extra lean burn is attained, which can increase the fuel efficiency remarkably. The stratified combustion mode is aimed for respecting the fuel efficiency, and is used when lower load and idle operations. It is preferable that the fuel spray at the stratified combustion mode is compact in order to concentrate the fuel spray around the ignition plug, and in case of the fuel spray when the fuel is highly pressurized because the spread of the fuel spray becomes smaller as the back pressure increases.
Conventionally, there are several alternative proposals for fuel injection valves in order to increase the aerification performance (fuel grain refinement) and the swirl performance.
For example, in Japanese Patent Application Laid-Open No. 8-296531 (1996), a swirler shaped in a hollow cylinder is placed at the lower part in the valve body, and a needle valve is inserted through the internal cylinder so as to be able to slide with the internal surface of the hollow cylinder, and a fuel injection chamber with its inner surface being tapered and its bottom surface being shaped in a spherical concave is formed at the down stream side of the valve sheet to which the needle valve contacts, and a injection port (fuel injection port=orifice) is formed so as to pass out through the center of the bottom face of the fuel injection chamber, and in addition, the orientation of the injection port is slanted to the axis (center line) of the valve body (fuel injection valve body) and a flat part is formed at the outside of the injection port so as to be at right angle to the injection port.
In Japanese Patent Application Laid-Open No. 7-119584 (1995), what is disclosed is that a swirl color (fuel swirling means) is placed so as to be located at the swirl nozzle (nozzle body) at the upper stream of the valve sheet, a suck hole shaped in a reverse cone is formed at the down stream of the valve sheet, an injection port (fuel injection port=orifice) is formed on the extension line from the suck hole, and that the center line of the suck hole and the center line of the injection port are identical to each other and those center lines are slanted to the axis of the swirl nozzle (fuel injection valve body). In this prior art, even in case of defining the inclination for the injection hole, the swirl reaches the injection hole as the rotational center of the swirl rotating on the plane orthogonal to the center line of the swirling flow traces on the linear locus along the center line of the injection hole. So far, the swirl loss in the suck hole becomes smaller and the swirl having a strong turning force is moved to the injection hole, by which the grain refinement of the fuel can be promoted as well as the spread of the spray in the combustion chamber becomes larger due to the increase in the spray angle, all of which ultimately leads to the increase in the efficiency of fuel combustion.
In case of in-cylinder injection type engine, the fuel injection valve body in the prior arts described above are generally located at the upper part of the cylinder, and by means that the fuel injection port are displaced toward the cavity of the piston head (at the opposite position to the ignition plug) from the longitudinal axis of the fuel injection valve body, and that the fuel is injected with deflecting toward the cavity, then the direction of the fuel spray is shifted to the ignition plug side by means of the shape of the cavity at the stratified combustion mode.
In Japanese Patent Application Laid-Open No. 5-33739 (1993), what is disclosed is that an air chamber is formed between the spray nozzle and the cover, the assist air from the air chamber is injected out into the swirl chamber in the tangential direction through the individual air injection hole, the fuel is directly injected from the injection hole into the engine cylinder as the injection fuel from the injection hole is forced to be swirled.
In Japanese Patent Application Laid-Open No. 6-221249 (1994), the injection angle of one of a couple of injectors placed in a single combustion chamber is made wider than the injection angle of the other of those injectors as well as the injector with a narrower injection angle is placed much closer to the ignition plug than the injector with a wider injection angle is, and that the injector with a narrower injection angle is used at a light-load operation and the injector with a wider injection angle is used at a high-load operation.
In the stratified combustion mode described above, it is important to concentrate the fuel spray around the ignition plug, and in the uniform combustion mode, it is important to spray the fuel uniformly and wholly in the cylinder, and furthermore, it is preferable to make smaller the grain size of the sprayed fuel mist commonly in the uniform combustion and the stratified combustion in order to reduce the time for vaporization. In addition, it is required to reduce the dispersion in the quantity of injected fuel.
In an internal combustion engine in which fuels are injected directly into the cylinder (the combustion chamber), the direction, shape, flow rate and flow velocity (the reachable distance of the fuel spray) of the fuel spray injected by the fuel injection valve influence much the concentration distribution of the mixed air in the combustion chamber at the ignition timing, and ultimately affect the engine performance.